The work flow I would use with that camera is just take your clips, and render them to a 1080-30p-XDCAM-EX.MFX profile. Then edit the xdcam clips, and keep the .mts around if you need them for some reason. Render your media to the same XDCAM profile. YouTube supports uploading that file directly, MP4 conversion is not needed.

3 - Render Edit project to Sony AVC.mp4 or XDCAM-EX.mxf, and upload directly to YouTube. XDCAM.MXF will smart render segments of edit timeline, so you gain back conversion time here.

Render profiles can be created to suit your needs, so if a format profile does not exist, create it. 1080-60P is one that is contemporary, but needs to be created under render settings. There is a customize template button in the render window.

Stay away from rendering to QuickTime formats in windows. Apple makes sure to keep their software gimped on the PC, for obvious reasons.

There is a utility available from Sony that allows FCP on the Mac the ability to edit XDCAM footage. So it is a good format for both. Of course like any religious conversation, there will be several passionate pleas for the their way of doing things. Sony AVC.MP4 @ 22-26MBS would work as well, xdcam is just more pro. DNxHD, or HDCAM-SR-Lite formats would be good as well if they are using AVID or Resolve.

Editing with an intermediate format in .MXF will perform better on the timeline and be more stable. There are performance optimizations in vegas for XAVC-Intra, HDCAM, and XDCAM 422/EX. Using source formats like .MP4, .MTS, and .MOV do not function as well on the timeline, and in some instances have bad limits on the amount of events you can have on a timeline. This optimization improves the amount of FX you can run without dropping FPS, and render times.

You can test this yourself by rendering test clips in the above formats, then dropping them on a timeline. When you scrub the clips with the cursor, you should see smooth fast animation, and no "..." after the frame counter in the preview window. Obviously do this in Best/Full preview. If you are seeing a series of still images, then that is not what you should be seeing. Still images means the system working hard to keep up with what you are asking for, and it can only show a few frames at a time.

You can setup another test with a couple clips dissolving with an FX applied. Then compare the frame rate in Best/Full. If you system is really fast, you may need to set the project settings to 32-bit FP Video Levels to increase the complexity of the playback. You could also just add more FX to the clips. Optimized formats will maintain playback speed or playback with higher frame rates.

Vegas is very accommodating and will work with whatever formats you throw at it, and not really complain. NLEs like AVID, FCP, or Resolve will ask you at certain points to optimize footage. Which at that time they convert media to an intermediate format they prefer.

If your source media is .MTS format or from standard consumer cameras /DSLR, you do not need the 32-bit FP video level setting in your project setup. Unless there is a specific reason you feel you need it. That setting will just slow down your renders. 32-FP mode is designed to work with 10-bit or greater video formats. Most consumer cameras, even 4K cameras, are 8-bit video sources.